Known methods of on-site chlorine generation have proven relatively suitable, although there have been problems relating to chlorine generating units for residential swimming pools and small to medium bodies of water (under 40,000 gallons). For the most part, known methods of on-site chlorine generation have not been adequate for treating large commercial swimming pools or large bodies of water.
Swimming pools, as well as certain other bodies of water, must be sanitized in order to be safe for use. Lack of proper sanitization results in damaged equipment, damaged pool surfaces, and allows water to become a breeding ground for disease and algae.
Swimming pool owners generally take care of the chemistry of the pool water in one of the following ways:
The residential pool owner hires a pool service company to come out once a week and bring the chemicals necessary to keep the water safe and sanitized.
The Board of Health will not allow a “once a week” treatment for commercial pools. The Board of Health requires that any commercial or public pool have some means on-site for automatically dispensing sanitizing chemicals into the pool water.
Common on-site chemical dispensing devices are: an adjustable liquid pump that takes liquid chlorine from a storage vat, and injects it into the pool's return line; a chlorine tablet holder that is installed into the return line that allows the tablets to be dissolved at an adjustable rate; and a powdered chlorine dispenser that automatically dumps powder into a container that has pool water circulating through it.
Some problems with these devices are that, because they are mechanical and exposed to the corrosive nature of pool chemicals, they are not very reliable, and require frequent service or replacement. Often the owner/operator resorts to adding chlorine into the pool by hand.
Another method for dispensing chlorine that has become accepted in recent years is to add salt to the pool and then to install an in-line chlorine-generating cell that will produce chlorine from the salt in the pool water.
Two of the Many Problems with this Type of Device are:
1. The amount of chlorine produced is too small to adequately deliver the amount of chlorine needed during a heavy swim load. As a result, it is a common practice to have a liquid chlorine dispenser as a backup; and
2. Since pool water commonly has a high amount of dissolved solids, the inline cells become fouled with hard water deposits, and consequently require frequent cleaning, service, and/or replacing.
Bromine dispensers are another method for dispensing sanitizing chemicals into a pool to be sanitized. Bromine is an accepted product for sanitizing pool water and can be provided as a tablet, or in stick form. Dispensed into the pool water, bromine will kill algae and bacteria, but is far more expensive than chlorine.
Another method, which has been outlawed in some areas because of extreme hazards associated therewith, is to have a pool service bring compressed chlorine gas to a pool site, and then to dispense it into the pool water. This is accomplished by submerging a manifold in the deep end of the pool, and then bubbling chlorine gas into the water from a portable gas cylinder. In addition to the danger of having compressed chlorine gas in a neighborhood, the addition of chlorine gas to pool water makes an acid that must be neutralized with a base product, such as soda ash. With this method, the extreme vacillation of pH and chlorine, from high to low, adversely affects the swimmer's health and safety, as well as causing bleaching of suntan, swimwear, and towels, and leads to green hair, irritated skin, and irritated eyes.
In addition, when the pH is below 7, and there is any copper in the pool's plumbing, copper oxide is formed, which causes a blue-green stain on the pool finish. When the pH of the pool rises above 8, minerals in the pool water deposit on the pool finish. These variations in pool water chemistry shorten the life of the pool's plumbing, equipment, and plaster finish.
In addition to the above problems, when concentrated commercial chemicals are used, it is easy to over-treat the pool water, and to get the chemistry out of balance. Out-of-balance pool water is the culprit that causes most surface-staining of plasters, and causes discomfort to swimmers.
Over the years, there have been a number of other devices and methods that have been marketed to assist in the sanitation of pool water.
For example, ultraviolet light is a sanitizing method which uses a clear plastic or glass cell containing an ultraviolet (UV) light. When the filtered pool water passes through the cell on its way back to the pool, the water is exposed to UV rays that can kill bacteria. The problem with this system is that it leaves no residual protection in the water. Consequently, if the water becomes contaminated after it leaves the ultraviolet light cell, bacteria in the water will not be killed until the water again passes through the cell. Chlorine is usually still used to provide the residual bacteria kill needed. The basic claim of the ultraviolet light system is that it will reduce the amount of chlorine needed to sanitize a pool.
Ozonators are another device for sanitizing pool water. This type of device uses high voltage to create ozone from the air, which is then injected into the pool water before returning it via the return line of the pool. Ozone kills bacteria, but does not stay in the water after the water is returned to the pool. It will reduce the amount of chlorine needed, but is not accepted by the Board of Health as a sole means of sanitizing pool water, because it doesn't leave a residual disinfectant or sanitizing agent in the pool water for a long enough time.
Copper/Sliver ionization is another method of sanitization. Copper and silver ions cannot remove organic matter, such as skin tissue, hair, urine, and skin flakes from water. Thus, another disinfectant, such as chlorine, needs to be used in addition to the copper and silver ions. Chlorine demand can be reduced by as much as 80% with the addition of copper and silver ions. In addition, copper and silver ions will stay in the water longer than most other sanitizing products, and are not affected by pH, heat, or sun. However, the process of killing bacteria and algae using copper and silver ions is slower than with other pool water sanitization methods. Copper/silver ions and chlorine make a good combination of sterilizing agents, but copper/silver ions are not sufficient as a sole agent for sterilizing pool water.
Commercial Chlorine Products:
Powder and Tablet Forms of Chlorine:
These forms of chlorine usually contain cyanuric acid, commonly called pool stabilizer. After the chlorine delivered by these products has dissipated from the pool water, the stabilizer remains. The effect of stabilizer is to slow down the reaction of chlorine so as to make the chlorine last longer in the pool. Too much stabilizer can inhibit the chlorine's ability to kill bacteria fast enough for the pool water to be safe for swimmers. Therefore, the Board of Health states that stabilizer concentrations over 75 ppm are unsafe, because such concentrations make the reaction of chlorine too slow to kill bacteria. This law prevents commercial pool owners from using pill, powder, and tablet forms of chlorine as the sole method for sanitation.
Another problem using commercial chlorine in the form of tablets and powders is that as much as 95% of the “chlorine” that is purchased is not chlorine, but instead consists of inert ingredients that the manufacturers add to their product to stabilize the chlorine and to give it shelf life. This can add a large amount of undesirable dissolved solids into the pool water, which can eventually cause staining of the pool finish, discomfort for swimmers, and can shorten the life of the filtering equipment.
The chemicals used in treating pool water are manufactured off-site, usually in a rural area away from the heavily populated cities. Products such as salt, stabilizer, calcium, soda ash, etc., must be transported to the chemical factory. After the pool chemicals are manufactured, they must be put in bottles or other suitable containers, labeled as “hazardous products”, and then shipped into cities and towns to be stored in warehouses. The products are then shipped in smaller amounts to the retail stores where they are purchased by the service companies or by the end user, and then are transported to the pool site where they are stored until they are used. A vehicle accident while transporting concentrated pool chemicals, or the improper storage of these chemicals, has resulted in the chemicals getting wet or mixed, which has caused fires, explosions, and the emitting of dangerous deadly gases often endangering children as well as adults.
Inline Chlorine Generators:
Over the years, there have been many attempts to generate chlorine at the pool site. Most of these devices require salt to be added to the pool water. Then, when the pool filter system is running, the salted pool water is directed through either an inline chlorine-generating cell, or a by-pass chlorine-generating cell.
To manufacture chlorine from pool water, hundreds of pounds of salt must be poured into the pool. Doing so raises the total dissolved solids, which can lead to deposits being precipitated out of the water onto the tile and pool finish.
When a saltwater pool is drained, or when water from the pool is backwashed into the sewer system, it makes the discharge water too: salty. This causes problems at the treatment plant, and it is now illegal to discharge water from salt-water pools into the sewer system, or to discharge into the drain gutters in some counties.
When an electric potential (also called “electrolysis”) is present in the pool water, the increased conductivity due to the salt in the pool water can lead to excessive corrosion on all metal parts of the pool circulating system. Most pool water has a higher amount of dissolved minerals than does tap water. This is due to the inert ingredients left over from pool chemicals that have been put into the pool, and to the evaporation of tap water which also leaves minerals in the pool water, resulting in “hard water”. When this hard water flows through chlorine-generating cells, the calcium and magnesium dissolved therein form deposits inside the cell on the cathode (the negative electrode). This reduces the efficiency of the cell, and necessitates cleaning of the cell by the operator, which is difficult and time consuming. If the cell is not cleaned, the build-up will continue to lower the efficiency of the cell, shorten its life, and eventually destroy it.
Another problem with this type of system is that, to make chlorine, the entire filtering system must be running to provide large amounts of constant water flow through the cell. This wastes a great deal of electricity, and does not give the operator the option of filtering less and chlorinating more.
Another problem with in-line chlorine generators is that when pool water temperature drops below 60°, the chlorine production is drastically reduced or terminated with an inline system.
Another problem with in-line chlorine generators is that the efficiency of an electronic cell operating in a mild salt solution is far less than the same electrolytic cell operating in saturated softened brine water.
Another problem with in-line chlorine generators is that when the pool owner changes the valves on his filtering system to use and heat his spa and forgets to shut “off” the inline chlorinator, all the chemicals being manufactured for the pool are directed to the spa, which only contains 500 to 800 gallons of water. In short order, the spa can become dangerously over-chlorinated and out of balance.
Still another problem with in-line chlorine generators is that in the event the filter pump stops, or for any reason the flow of water stops going across the inline chlorine generator's electrodes and the unit is still running, an accumulation of hydrogen gas is created. This pocket of hydrogen gas is extremely dangerous, and can be ignited by sunlight or by the electrodes themselves, resulting in a powerful explosion.
Considering the need for daily chlorination and the increasing cost of energy, as well as the problems caused by adding large amounts of salt to the pool water, these inline chlorine generators are neither able to provide the maximum protection, nor are they cost effective.